Dual-Emissive Carbon Quantum Dot-Tb Nanocomposite as a Fluorescent Indicator for a Highly Selective Visual Detection of Hg(II) in Water

We report very fast, green, and large-scale synthesis of amino-functionalized carbon quantum dots (CQDs) using a domestic microwave to investigate CQD-Tb-based dual emission for visual detection of toxic Hg²⁺. Citric acid and p-phenylenediamine are used as precursor materials to synthesize the CQD, which shows excitation-independent blue luminescence. To achieve the dual emission, Tb-containing CQD is synthesized in a very easy and cost-effective way. These dual-emissive fluorescent materials have been successfully used as a fluorescent indicator for visual detection of toxic Hg²⁺ metal ions. An instant color change from blue to green in the presence of a very low amount of Hg²⁺ under a UV lamp (?_365nm) is observed. The material is highly sensitive and selective toward detection of mercury ions in the presence of other metal ions. The photoluminescence quenching mechanism (photoinduced electron transfer process) has been explained using an electronic band diagram supported by zeta-potential and time-correlated single photon counting measurements.